* struct.c (rb_struct_define_without_accessor_under): added.
  This function is similar to rb_define_class_under() against
  rb_define_class().
* include/ruby/intern.h: add a declaration of this function.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42725 b2dd03c8-39d4-4d8f-98ff-823fe69b080e